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Of course you can base the amount you spend on links based on an ROI figure. But what do links cost? A thread at WebmasterWorld named Is this a reasonable amount to pay for links, discusses just that.
It is obvious that link development in the US will cost at least 4x as much as link development in India. :)
update: Looks like the thread I linked to above, has been warped into a different thread. No I am not crazy.
